Calc is an interactive calculator which provides for easy large numeric
calculations, but which also can be easily programmed for difficult or long
calculations using a C-like language featuring variable declarations,
expressions, tests, labels, loops, file operations, and function calls,
and with a rich set of builtin mathematical and programmatic functions.

It can accept a command line argument, in which case it executes that single
command and exits. Otherwise, it enters interactive mode. In this mode, it
accepts commands one at a time, processes them, and displays the answers. In
the simplest case, commands are simply expressions which are evaluated.
